Intraocular lenses (IOL's) are a well-known type of surgical implant used to replace the natural lens of an eye which has been damaged as a result of trauma or disease. Such IOL'S typically comprise an optic and at least one fixation member attached to the optic. The fixation member functions to position the optic in the correct optical alignment within the eye. Many fixation members are of filamentary form, and are attached to the optic at or near the periphery of the optic.
It is conventional practice to construct the optic of a hard biocompatible polymer, such as polymethylmethacrylate (PMMA). More recently, it has been proposed to construct the optic from a relatively flexible or deformable material. When so constructed, the optic can be rolled or flexed into a relatively small cross-sectional configuration to permit it to be inserted through a relatively small incision into the eye to thereby reduce the trauma and likelihood of infection from the surgery.
The fixation members are constructed of a resilient material, typically polypropylene. In some IOL'S, the fixation members are integrally formed with the optic. In other types of IOL'S, various methods of attaching the fixation members to the optic have been devised.
A common method of attaching requires drilling two small intersecting holes in the edge portion of the optic. A proximal end portion of the fixation member is inserted into one hole and a heated rod is inserted through the other of the intersecting holes. The heated rod melts the proximal end portion of the fixation member where contacted. The fixation member is fed into the hole as the melted material flows into the second intersecting hole, causing a mechanical interlock when the material solidifies. Great precision is required in the drilling of the intersecting holes. Also characteristic of the IOL'S made according to this method is the potential of debris-trapping cavities remaining from a less-than-perfect filling of the holes in the optic by the melted portion of the fixation member.
The attachment of the fixation members to the optic is particularly troublesome when the optic is constructed of soft or deformable materials, such as silicone. When the deformable optic is folded or rolled prior to insertion through the incision into the eye, flexure of the optic creates a likelihood that the fixation member will become detached from the optic. If this occurs, it not only renders the IOL useless, but also is a potential hazard to the patient. The soft optic materials, such as silicone, do not have sufficient rigidity to be used as an integral fixation member or haptic.
It is known to attach the fixation members to a large resilient, circular ring and to mold the soft optic material over the ring so that the ring is concentric with the optic and extends along a peripheral region of the optic. However, for foldable optics, this construction precludes the use of rigid or non-foldable materials for the ring and requires the dedication of a large diameter annulus of the optic to capture the ring.